The present invention relates to an apparatus for the supply and/or branching of a secondary flow into and/or out of a main flow of a medical fluid comprising a fluid guidance body in which at least one main passage open to one side and at least one secondary passage opening into the main passage are provided and comprising a covering film which is disposed above the open side of the main passage on the fluid guidance body, with the opening of the secondary passage into the main passage being closable by the covering film. The invention further relates to a valve actuator for such an apparatus having a main plunger surface to press on the covering film at the edges of the main passage and a secondary plunger surface to press the covering film onto the opening of the secondary passage.
So-called disposable cassettes of the membrane type are known, for example from WO 97/09074, in which medical fluids such as dialysis fluid flows into passages open to one side. The passage walls and the surfaces disposed between the passages are formed by a cassette body made as a rule in injection moulding. The passages open to one side are sealed by a covering film which is placed on, for example by being welded on along the passage edges or by pressing on, optionally onto passage edges made in an elevated manner.
A machine into which such a disposable cassette is inserted as a rule includes the actuating system for measuring functions, pump functions and valve functions and areally clamps the cassette together with the covering film disposed thereon. The edge layer of the surface on the machine side which lies on the covering film consists as a rule of an elastomer.
In particular with disposable cassettes which are part of an extra-corporeal blood circulation for extra-corporeal blood treatment, the requirement exists in a technical process respect that alternatively fluids such as infusion solutions, medicines, heparin, substituate and the like should be dosed in or fluid samples taken out of the passages. Valve positions are required for this purpose in order to connect the main passage, through which the medical fluid flows, to a corresponding secondary passage. This secondary passage is regularly closed since the dosing in or sampling only take a short time.
Such devices are subject to a variety of demands which have not yet been satisfactorily solved by the prior art. Generally, the functions to be met should be achieved with a compact arrangement. When the secondary passage is transposed into the main passage, however, problems result with respect to a low turbulence and low resistance flow of the medical fluid in the main passage, in particular when this is blood. Furthermore, the covering film in known arrangements tends to fatigue as a result of the secondary passage being kept closed over a long time.
It is therefore the underlying object of the present invention to provide an improved apparatus of the kind first given and an improved valve actuator of the kind first given, to avoid the disadvantages of the prior art and to further develop these in an advantageous manner. The dosing in and the sampling should preferably be made possible in a securely closing and low wear manner with a simple, compact and low cost arrangement without lasting interference to the flow relationships of the medical fluid.
This object is solved in accordance with the invention by an apparatus for supplying and/or branching off of a secondary flow into and/or out of a main flow of a medical fluid, which includes a fluid guide body, in which at least one main passage open to the side and at least one secondary passage opening into the main passage are provided. A covering film is disposed on the fluid guide body above the open side of the main passage, and the orifice of the secondary passage into the main passage can be closed by the covering film. The secondary passage is formed such that the main passage is substantially free of wake space in the region of the orifice of the secondary passage. The said object is solved in accordance with the invention by a valve actuator for the apparatus which includes a main plunger surface to press the covering film onto the rims of the main passage and a secondary plunger surface to press the covering film onto the orifice of the secondary passage, and wherein the main plunger surface and the secondary plunger surface are in the same plane.
The secondary passage, its orifice and the main passage are therefore designed in a flow-favourable manner such that a main passage flow which is free of wake space arises in the region of the orifice of the secondary passage and does not characteristically differ from the flow in the valve-free sections of the main passage. These flow qualities substantially improve the haemocompatibility of the apparatus.
In order to also achieve a low vortex and low resistance flow of the medical liquid in the main passage in the region of the secondary passage feed, the outside of the wall of the secondary passage section located in the main passage advantageously has a rounded shape favourable for flow and free of corners or edges which cause wake spaces and vortexes. The outside of the secondary passage section located in the main passage can in particular have a streamlined form in accordance with the flow direction of the main flow in the main passage. xe2x80x9cStreamlined formxe2x80x9d is here understood to mean a shape with a favourable circulation with which separations and vortexes or turbulences are effectively reduced and, in the ideal case, fully prevented. Unlike an only circular cross-sectional shape, vortexes and bubbles are effectively prevented by the streamlined shape and a laminar circulation of the secondary passage disposed in the main passage achieved. The flow resistance can be kept small despite the fact that the secondary passage extends in the main passage. The outer contour of the secondary passage is in particular of streamlined shape such that an eddy-free and laminar circulation is ensured which does not characteristically differ from the flow in the valve-free main passage sections. These flow qualities contribute in particular to the haemocompatibility of the apparatus for the event that blood flows through the main passage.
The ratio of the section length to the section width of the streamlined shape can generally be selected differently and matched to the circumstances of the main passage flow. In accordance with a preferred embodiment, the extent of the outside contour of the secondary passage located in the main passage in the main flow direction is at least twice as large as the extent of the outside contour transverse to the main flow direction.
In a further development of the invention, the outside contour of the secondary passage has an acutely tapering separation edge at the leading side and the trailing side, at least at the trailing side. The outside contours of the secondary passage can have a curvature continuously. The separation edge itself can also be rounded. The leading edge can be designed much rounder than the trailing edge, as is known from hydrofoil sections or drop sections. A laminar circulation is maintained in this way and connected to the advantage that the rounded leading edge offers fewer possibilities for stringy or sticky fluid components of the main flow to stick at the leading edge. A symmetrical design of the leading edge and the trailing edge can be advantageous if the flow in the main passage should run through this in changing directions.
In accordance with a preferred embodiment of the invention, the fluid guide body is characterised in that the orifice of the secondary passage into the main passage is substantially disposed in the plane set by the adjacent rims of the main passage. The end of the secondary passage at the orifice side is vertically coincident with the passage rims in the main passage and is thus in the plane of the covering film when this is stretched from the passage rims over the main passage. The covering film does not need to be pressed into the main passage in order to close the secondary passage. No impairment of the main flow takes place with a closed secondary passage. Fatigue of the covering film is substantially reduced and almost precluded since no stretching of the film is necessary in order to press this onto the secondary passage orifice. At the same time, the covering film can be placed over the main passage tautly and free of creases, whereby closing problems due to creases in the covering film are avoided.
In a further development of the invention, the orifice of the secondary passage into the main passage forms a planar, flat valve seat. Misalignments between the passage orifice and the valve plunger on the machine side thereby become insignificant and generous positioning tolerances are made possible between the disposable and the machine actuator, which reduces the costs due to reduced accuracy demands and increases the closing security.
In accordance with a preferred embodiment of the invention, the longitudinal axis of the secondary passage opens perpendicularly onto the flow direction of the main flow and in particular perpendicular to the covering film. The secondary passage can form a funnel in the main passage which extends from the base of the main passage up to its open side. The secondary passage comes from the rear side of the fluid guide body opposite to the open side of the main passages. Due to the side change of the secondary flow opening into the main flow, the rear side of the fluid guide body can likewise be used for flow passages which can even cross over the front-side main passages. A more effective use of the constructional space for the functions of the apparatus is thus possible. The secondary passage can be guided at the rear of the body either coaxially or at an angle into another flow tube which can be made in a technical injection moulding manner in a suitable embodiment. This other end of this tube can be formed as a male connector or as a hose permanent connection connector.
The section of the secondary passage which is in the main passage can be arranged at a different position there. It can extend along a wall of the main passage so that only a part of the secondary passage wall projects over the main passage wall. With such an embodiment, only this part of the secondary passage outer contour is accordingly formed in streamlined manner. The projecting secondary passage wall forms a streamlined half-section.
To facilitate the production and the sealing of the passages, it is preferably provided that the seal line around the orifice of the secondary passage, along which the secondary passage can be closed by the covering film, is spaced from the seal lines along which the main passage can be closed by the covering film.
In accordance with a preferred embodiment of the invention, the secondary passage extends in self-supporting manner in the main passage. The secondary passage in the main passage is in particular arranged symmetrically relative to this. The secondary passage is flowed around in the main passage in a favourably flow similar to a bridge support or an island. Since the orifice of the secondary passage contacts the wall of the main passage formed by the covering film and thus closes, the main passage flow is not influenced by the secondary passage orifice in its closed state as this is not flowed around at all by the main passage flow.
The main passage is preferably shaped in a favourable flow manner around the secondary passage, in particular such that the flow cross-section in the main passage also remains approximately constant in the region of the secondary passage which opens in. Changes in the flow speed are avoided in this way. When blood is the fluid flowing in the main passage, it has moreover surprisingly been shown to be favourable for the flow cross-section in the main passage to be somewhat larger in the region of the opening secondary passage than in the main passage before and after this. In this respect, an enlargement of 40% is advantageous, in particular of 25%.
As a consequence of the vertically coincident arrangement of the secondary passage orifice to the main passage rims, a common planar plunger surface can be provided as the valve plunger to press on the covering film which presses the covering film both onto the rims of the main passage and onto the secondary passage orifice. The common, planar plunger surface allows generous positioning tolerances when setting the plunger actuator onto the covering film without reducing the closing reliability. Furthermore, the planar valve seat on the machine side means that the valve position does not make itself felt there at all geometrically and is thus neither at risk of collision nor of contamination. Furthermore, only a very slight deformation of the covering film and of the machine membrane provided on the valve actuator side results with the closed position of the valve actuator provided for most of the time. The circumstances reduce the actuating forces and the fatigue. Furthermore, a plastic deformation of the disposable film is avoided which precludes crease formation and increases the closing reliability.
In a further development of the invention, the plunger surface for the secondary passage orifice is designed movably relative to the main plunger surface for the main passage rims. In can be moved by means of an actuating part. The movability of the plunger surface section for the secondary passage orifice can be achieved by various designs of the plunger surface. A preferred embodiment consists of the whole plunger surface being formed by an elastomer plate.
The actuating part and thus the corresponding section of the plunger surface on the machine side is raised from the covering film on the fluid guide body in order to open the secondary passage orifice. In this respect, the covering film is raised from the orifice of the secondary passage so that the secondary passage is brought into flow communication with the main passage. The lifting of the covering film takes place automatically as a result of an overpressure of the main flow or of the secondary flow. In a further development of the invention, a vacuum can also be disposed between the plunger surface of the valve plunger and the covering film so that the covering film is actively raised on the moving away of the plunger surface. In this way, the fluid connection between the secondary passage and the main passage can be controlled independently of pressure relationships in the cassette-side flow passages.
Particular advantages result in the use of the above-said apparatus in conjunction with blood, that is in the supply of a medical fluid into a bloodstream and/or the sampling from a bloodstream. The streamlined shape of the secondary passage prevents the stalling of the bloodstream in wake spaces or flow shadows behind the secondary passage and a blood-damaging formation of turbulence.
The apparatus of the invention for the feed and/or branching off of a secondary flow into and/or out of a main flow is used particularly advantageously as part of an extra-corporeal blood circulation for extra-corporeal blood treatment. Such a blood treatment can, for example, comprise haemodialysis, haemofiltration, blood cell separation or blood adsorption. In this application, the apparatus is advantageously designed as a disposable for throw-away use. The valve actuator of the invention is in this case usually part of the blood treatment machine which controls the flows of the fluids involved.